Higher performance of chips, an increase in the number of layers of wiring boards, a wider spread of lead-free solders with high melting points, and so forth require electronic components, such as printed circuit boards and semiconductors, to have high heat resisting properties (glass transition temperature). To improve the speed of processing, circuit currents with higher frequencies are used, so peripheral members are polarized to cause transmission loss. Thus, there is an increasing demand for low-dielectric-constant materials, which are not easily polarized.
Known examples of resins conventionally used for printed circuit boards and semiconductor sealing materials include ortho-cresol novolac type epoxy resins and dicyclopentadiene type epoxy resins. While ortho-cresol novolac type epoxy resins have high heat resisting properties, they have high dielectric constants. This disadvantageously limits the use thereof, depending on the applications. While dicyclopentadiene type epoxy resins have low dielectric constants, they have insufficient heat resisting properties, depending on the applications. Thus, there has been a demand for a resin with good heat resisting properties and a low dielectric constant.
Patent Literature 1 discloses a phenolic resin prepared by allowing a compound having a benzene ring with one or more hydroxy groups to react with a dialdehyde compound and a formaldehyde-containing cross-linkable compound; an epoxidized phenolic resin prepared by epoxidation of the phenolic resin; an epoxy resin composition containing the phenolic resin and the epoxidized phenolic resin; and a cured product (cured epoxy resin) containing the epoxidized phenolic resin.